The Rear Knuckle Bushing Kit for the ND Miata provides you with a smooth articulating, deflection and compliance eliminating solution to take all of the "street-car" mushiness out of the rear of your suspension. The rear knuckle bushings in the ND Miata are rubber injected bushings with metal sleeves in them. While this does provide for a compliant ride, this is not what you desire when you are pushing the vehicle to its limits. When pushing the car to the limit, the OEM bushings will bind and deflect causing unwanted changes to your alignment as your round corners, making it difficult to hold the car at peak grip. Replacing with a full spherical solution will eliminate all artificial spring rate and mushiness from the rear of your suspension, and allow the car you to drive the tires to their full potential grip